1. Field of the Invention
The present invention relates to a noise reduction device which reduces or eliminates a noise of a wireless signal received by a wireless communication unit. More particularly, the invention relates to a noise reduction device suited for reducing or eliminating a noise in a wireless network or the like in a bad communication environment and a wireless LAN base station apparatus using the noise reduction device.
2. Description of the Related Art
Conventionally, various types of systems that hold wireless communications are faced with unavoidable noise influence problems. Recently, a wireless LAN system has been developed. This system connects a server to a personal computer and allows the personal computer to hold data communication or the like.
In the system of this type, the personal computer is disposed in the interior of a building and the wireless LAN base station is also disposed in the same interior. Due to this, the wireless LAN base station is often located adjacent various noise sources employed in the interior. Examples of the noise sources employed therein include home electric appliances. If the wireless LAN bas station is disposed, in particular, adjacent a noise source that generates a noise at a frequency in a band equal to a frequency band of the wireless LAN base station, a wireless environment is disadvantageously deteriorated. Examples of the home electric appliance that generates a noise in a frequency band equal to that of the wireless LAN base station include a microwave oven. The wireless LAN base station is often disposed in the vicinity of the microwave oven.
As a conventional noise prevention method for the wireless LAN system, there is known a diversity system. According to this diversity system, two antennas are employed and a signal is received from one of the antennas that has a better sensitivity.
Further, as described in Japanese Patent Publication No. 2000-293965 A (paragraphs 0011 to 0013 and FIG. 1), a noise that is estimated to occur is sampled in advance and the sampled noise is written to a nonvolatile memory. When a noise occurs, the sampled noise is read from the memory and the noise is subtracted from a voice signal into which the noise of the same type is mixed.
However, the conventional diversity system is not intended to reduce a noise. For this reason, if a noise source is located near a wireless communication unit or system, the wireless communication unit or the system is influenced by a noise, with the result that the diversity system is disadvantageously incapable of attaining a noise reduction effect.
Furthermore, in the method described in Japanese Patent Publication No. 2000-293965 A, the noise reduction effect can be attained only for the noise that is estimated in advance. If the location of the device is moved, etc. and a noise other than the estimated noise is mixed into a signal, the method is disadvantageously incapable of attaining the noise reduction effect.